1. Field of the Invention
The present invention relates to a linear motor and a linear compressor using the same. More particularly the present invention relates to a linear motor and a linear compressor using the same which removes a gap of a magnet and an inner core and in which the inner core is formed to be longer than an outer core.
2. Description of the Background Art
In general, a linear motor generates a linear reciprocating force and applies the force to a linear reciprocating object (hereinafter, referred to as “a moving body”) such as a piston and generally includes a stator in which a coil is provided and a rotor for performing a linear reciprocating motion of the moving body by a reciprocal action with the stator.
Recently, a linear compressor, etc. for compressing a fluid such as a refrigerant gas using the linear motor has been developed.
The stator includes a bobbin, a coil wound in the bobbin, an outer core radially provided in the bobbin, and an inner core provided to be spaced at the inside of an outer stator.
The rotor is a magnet which performs a linear reciprocating motion between the outer core and the inner core by an interaction with a magnetic force generated when a current is applied to the coil.
The magnet has an outer gap g1 between the magnet and an inner circumferential surface of the outer core and an inner gap g2 between the magnet and an outer circumferential surface of the inner core to perform a linear reciprocating motion between the outer core and the inner core.
A force (output) of the linear motor is determined by a motor force constant (a) and a current value (i) applied to the coil, where the motor force constant is proportional to a magnetic flux density (Bm) within a gap by the magnet, so that efficiency of the motor improves as a magnetic flux density (Bm) within a gap by the magnet increases.
Here, as shown in Equation 1, the magnetic flux density (Bm) within the gap becomes large as the outside gap (g1) and the inside gap (g2) become small.Bm=Br×t/2(g1+g2+t)   <Equation 1>where Br is a magnetic flux density (characteristic) within a magnet, t is a thickness of the magnet, and 2(g1+g2+t) is a gap of a linear motor.
That is, a force (output) of the linear motor and the linear compressor using the linear motor becomes large as a gap of the linear motor becomes small.
However, in a conventional linear motor and a linear compressor using the linear motor, because there are gaps in the inside as well as the outside of the magnet, a magnetic resistance for disturbing a magnet force becomes large. Thus, there is a problem that an using amount of the magnet increases to improve their output and their productivity is low because the inside gap as well as the outside gap should be managed to obtain a stable motor performance.